The present invention relates to an industrial robot of articulated type.
Conventionally, as an automatic machine for conducting operation such as painting or coating, welding or the like in place of operators, there is used an industrial robot in which an operational program is modified or altered thereby being capable of flexibly coping with various works. Among various industrial robots, an industrial robot of articulated type is well utilized which moves closer to man.
The conventional industrial robot of articulated type will be described below with reference to FIG. 10 of the attached drawings.
FIG. 10 is a perspective view showing the industrial robot of articulated type. The industrial robot has its principal components which include a base 1, a swing base 2 mounted on the base 1 and angularly movable about an axis a, a first arm 3 mounted on the swing base 2 in a straddle manner and angularly movable about an axis b which is perpendicularly intersected with the axis a, a second arm 4 arranged such that its center line exists in a plane including the axis a, the second arm 4 being mounted to a forward end of the first arm 3 in a straddle manner and being angularly movable about an axis c which is parallel to the axis b, a wrist drive section 5 mounted to a rearward end of the second arm 4 so as to extend rearwardly with respect to the axis c, and a wrist mechanism 6 mounted to a forward end of the second arm 4 and driven by a motor which is arranged within the wrist drive section 5.
The wrist mechanisms 6 comprises a case 7 mounted to the forward end of the second arm 4 and angularly movable about an axis d which is parallel to the axis c, a case 8 mounted to the case 7 and angularly movable about an axis e which is perpendicularly intersected with the axis d, and an attaching section 9 having mounted thereon a working tool or the like. The attaching section 9 is mounted to the case 8 and is angularly movable about an axis f which is perpendicularly intersected with the axis e.
Within the wrist drive section 5, three motors for driving the wrist mechanism 6 are arranged in side-by-side relation on a center line of the second arm 4.
As will be apparent from the above description, the industrial robot has six degrees of freedom. Accordingly, it is possible to operate the working tool or the like mounted to the attaching section 9 under such conditions that the working tool or the like is located at any position and is oriented toward any direction if the working tool or the like operates within an operational range. Further, since the motors for driving the wrist mechanism 6 are arranged rearwardly with respect to the axis c of the center of rotation of the second arm 4, the weight of the motors acts as a counterweight so that the counterweight cancels moment due to the weight of the second arm 4 and the weight of the wrist mechanism 6. Thus, the capacity of the motor for driving the second arm 4 can be reduced.
However, the conventional industrial robot described above has points to be improved as follows.
First, the first arm 3 and the second arm 4 are mounted respectively on the swing base 2 and the first arm 3 in a straddle manner. Accordingly, if the first arm 3 or the second arm 4 is angularly moved largely, the first arm 3 and the swing base 2 or the second arm 4 and the first arm 3 interfere with each other. For this reason, the angularly moving angle of the first arm 3 or the second arm 4 is restricted small so that the operational range of the robot is reduced. For instance, in FIG. 10, if the second arm 4 is angularly moved downwardly, the second arm 4 interferes with a recess 10 which is formed at the forward end of the first arm 3. Accordingly, it is impossible for the robot to take such a posture that the center line of the first arm 3 is brought substantially parallel to the center line of the second arm 4. Further, if the second arm 4 is angularly moved upwardly, the lower face of the wrist drive section 5 interferes with the first arm 3. Thus, the robot cannot take such a posture that the center line of the first arm 3 is substantially coextensive with the center line of the second arm 4.
Secondly, there are two confined portions designated by the reference characters K.sub.1 and K.sub.1, and two confined portions designated by the reference characters K.sub.2 and K.sub.2 in FIG. 10. For example, when the robot is used in painting operation, the robot is located within atmosphere in which a lot of paint scatters. Thus, the paint enters through the confined portions K.sub.1 and K.sub.1 and K.sub.2 and K.sub.2. For this reason, maintenance must frequently be done such as cleaning or the like of the interior. Moreover, in order to protect bearings against foreign matters or the like. seal material must be interposed between each pair of members or components. Alternatively, connecting sections must, as a whole, be covered with elastic or resilient material such as, for example, rubber membranes formed into bellows. Thus, the construction is complicated, assembling operation at manufacturing of the robot is difficult, and maintenance operation is not easy such as replacement, cleaning or the like of the aforesaid seal materials and so on.
Thirdly, a plane including the axis e does not include the axis a, and the plane and the axis a are parallel to each other, but are offset from each other by a length by which the case 7 projects from the side surface of the second arm 4. For this reason, in transformation computation between the orthogonal coordinates and the articulated coordinates for controlling the robot in a CP (Continuous Pass) manner, an offset amount must always be considered, so that the computation is complicated. This produces disadvantages such as an increases in a capacity of memory used in computation in a control device, increase of computation time, and so on.
Fourthly, since the first arm 3 and the second arm 4 are mounted respectively on the swing base 2 and the first arm 3 in a straddle manner, the bearings are necessary on both sides of each proximal portions of the first or second arm, which causes the complicated structure and the increased weight thereabout.
Fifthly, it is necessary to arrange cables for providing the motors for driving said wrist mechanism 6 with current, and the cables are usually arranged through said first arm 3. However, since the second arm 4 is supported by the first arm 3 in a straddle manner, it is difficult to draw the cables out from the first arm at a center of the angular movement of the second arm. This means that, when the second arm rotates, the cables are repeatedly extended and released which may cause the cables disconnection.